There have been known game systems in which an operation timing of an operating unit disposed in an input device is indicated to a player in tune with a rhythm of music. Of the game systems, there is a game system including an obstructing device that hides a part of an operation indication mark used to indicate an operation timing during the progress of a game (for example, see Patent Literature 1). Besides, another background art related to the invention is disclosed in Patent Literature 2.    Patent Literature 1: Japanese Patent No. 3031676 and Patent Literature 2: Japanese Patent No. 2922509.